Nuclear magnetic resonance spectrometer with jointly functioning external and internal resonance stabilization systems

ABSTRACT

A nuclear magnetic resonance spectrometer comprising an electromagnet accommodated in a housing with coils disposed within the magnetic field between the poles of the electromagnet. The electrical axes of the coils are oriented perpendicularly to the pole faces of the electromagnet. The coils are connected to the output of an internal nuclear magnetic resonance stabilization system. An analytical nuclear magnetic resonance probe is disposed in the zone defined by the coils and connected to the input of the internal nuclear magnetic resonance stabilization system. A reference nuclear magnetic resonance probe is disposed within the magnetic field of the electromagnet and is located so as to be outside the zone defined by the coils. An external nuclear magnetic resonance stabilization system is connected to the reference nuclear magnetic resonance probe and nuclear magnetic resonance signals derived from the analytical nuclear magnetic resonance probe are recorded. The external and internal stabilization systems operate simultaneously.

United States Patent 1191 [111 3,777,254 Kleiman et al. 1 Dec. 4, 1973NUCLEAR MAGNETIC RESONANCE 2/1969 Nelson 324/.5

Filed: Mar. 12,1971

Appl. No.: 123,915

Related us. Application Data Primary Examiner-Michael J. LynchAttorney-Waters, Roditi, Schwartz 81. Nissen [57] ABSTRACT A nuclearmagnetic resonance spectrometer comprising an electromagnet accommodatedin a housing with coils disposed within the magnetic field between thepoles of the electromagnet. The electrical axes of the coils areoriented perpendicularly to the pole faces of the electromagnet. Thecoils are connected to the output of an internal nuclear magneticresonance stabilization system. An analytical nuclear magnetic resonanceprobe is disposed in the zone defined by the coils and connected to theinput of the internal nuclear magnetic resonance stabilization system. Areference nuclear magnetic resonance probe is disposed within themagnetic field of the electromagnet and is located so as to be outsidethe zone defined by the coils. An external nuclear magnetic resonancestabilization system is connected to the reference nuclear magneticresonance probe and nuclear magnetic resonance signals derived from theanalytical nuclear magnetic resonance probe are recorded. The externaland internal stabilization systems operate simultaneously.

3 Claims, 1 Drawing Figure Reporter J flsclllagraph [63] Continuation ofSer. No. 789,887, Jan. 8, 1969,

abandoned.

[30] Foreign Application Priority Data Jan. 15, 1968 U.S.S.R 1,2l0,942

[52] US. Cl 324/-5 R [51] Int. Cl. G01n 27/78 [58] Field of Search324/.5 R, .5 A, .5 AC, 324/.5 MA, .5 H

[56] References Cited UNITED STATES PATENTS 3,388,322 6/1968 Anderson324/.5

170 f amplifier" AF blur/r 0 NUCLEAR MAGNETIC RESONANCE SPECTROMETERWITH JOINTLY FUNCTIONING EXTERNAL AND INTERNAL RESONANCE STABILIZATIONSYSTEMS This Application is a continuation of copending application Ser.No. 789,887 filed Jan. 8, 1969 and now abandoned.

The present invention relates to spectrometers operating on theprinciple of nuclear magnetic resonance.

Known in the art are nuclear magnetic resonance spectrometers (NMRspectrometers) comprising NMR analytical and reference probes placedwithin the magnetic field of the magnet pole gap. The NMR analyticalprobe serves an an input member of the NMR control system for theinternal stabilization of the magnetic field, the output member of saidcontrol system being constituted by coils disposed on the magnet poles.The NMR reference probe serves as an input member of the NMR controlsystem for the external stabilization of the magnetic field whose outputmember is constituted by the abovementioned coils which are included, asstated above, in the NMR control system adapted for the internalstabilization of the magnetic field (see, for example, JNM-SH-60 HighResolution NMT Instruments manufactured by the Japan Electron OpticsLaboratory Co., Ltd).

The external stabilization system of said NMR instruments ensures themagnetic field stability sufficient for solving the majority of everydayproblems in NMR spectroscopy. However, when performing-precisionexperiments in which the accuracy of measuring chemical shifts orspin-spin splittings should be better than 0.2-0.1 cps, in case thespeed of spectrum recording is less than 0.2-0.1 cps/sec, and in someother experiments the internal stabilization NMR control system is to beused.

An essential disadvantage of the aforesaid NMR instruments resides inthat their internaland external stabilization NMR control system cannotoperate simultaneously, since the same coils are employed as the outputmembers thereof. For the instrument to be operable with the internalstabilization system its external stabilization system should be cutoff. Considerable time is required for making the internal stabilizationsystem operative again, since the choice of the line to be used forstabilization and the feeding of this line signal into the circuit arecarried out under the conditions of a relatively low stability and, as amatter of fact, almost gropingly. As to the'resolution control,replacement of the samples etc, all such operations are to be performedeither without the stabilization of the resonance conditions, or afterthe instrument has been switched over to operate with the externalstabilization system. These factors involve considerable waste of timeand are responsible for a sharp decrease in the efficiency of labour.

It is therefore an object of the present invention to eliminate theabove disadvantages.

The principal object of the present invention is to provide a NMRinstrument which will ensure simultaneous operation of the external andinternal NMR stabilization systems with a minimum time required forpassing over from one type of work to another.

Said specific object is accomplished due to the fact, that in thepresent NMR spectrometer comprising an analytical NMR probe and areference NMR probe placed within the field of a magnet, of which thefirst probe is connected with the internal NMR stabilization system andthe secondwith the external NMR stabilization system, according to theinvention, arranged within the magnetic field of the magnet are magneticfield correction coils that are connected with the output of theinternal stabilization system, the electrical axes of said coils beingoriented perpendicular to the magnet pole faces, the analytical NMRprobe being disposed within the zone defined by said coils, and thereference NMR probe being arranged outside zone.

Such a constructive location of the probes and actuating elements of theexternal and internal NMR stabilization systems insures simultaneousfunctioning of these systems, since there exists only a weak connectionbetween the stabilization systems.

The connection in this case is to be understood as follows. Fluctuationsin one of the systems, e.g. in the internal system, cause a stabilizingreaction therein. This reaction due to the presence of the weakconnection causes fluctuations in the other systems (external). The

reaction of the actuatingcoils of theexternal stabilize tion systemcauses a reduction of fluctuations in the sample under'test.

Given hereinbelow is a description of an exemplary embodiment of theinstrument of the invention, to be had in conjunction'with theaccompanying drawing, wherein the block-diagram of the NMR spectrometeris presented.

The spectrometer according to the invention comprises an electromagnet1, systems of external and internal stabilization, a main NMR probe 2,an auxiliary NMR probe 7, a high-frequency unit for irradiating thesamples of said probes with high-frequency energy at a resonancefrequency, modulators and a device for registering the NMR signals, anda device (,not shown in the drawing) for controlling the temperature ofthe sample under test during temperature tests.

The internalNMR stabilization system consists of a RF amplifier 3connected to NMR probe 2. The output of the RF amplifier is connectedvia an aplitude discriminator or detector 18 to the input of an AFamplifier 4, the output of which is connected via a synchronous detector19, to the input of a d.c. amplifier 5. Connected to the output of theamplifier 5 are coils 6 adapted to correct the magnetic field anddisposed within the magnetic field between the poles of theelectromagnetic l, the axes of said coils being oriented perpendicularto the pole faces of the electromagnet 1. The NMR probe 2 is located soas to be within the zone defined by the coils 6.

The external NMR stabilization system comprises an RF amplifier 8 whoseinput is connected to auxiliary or reference NMR probe 7. The output ofRF amplifier 8 is connected, via an amplitude detector 20, to the inputof an AF amplifier 9, whose output is connected via a synchronousdetector 21 to the input of a d.c. amplifier 10. The output of the d.c.amplifier 10 is connected with the'actuating coils '11 of the externalstabilization system which are arranged on the poles of theelectromagnet l. The NMR probe 7 is located so as to be outside the zonedefined by the coils 6.

The device for recording the NMR signals comprises a recorder 14 and anoscillograph 13 connected, via a d.c. amplifier 23 and a synchronousdetector 22, to the block of AF amplifiers 12. The block of amplifiers12 is coupled, via the amplitude detector 18 and the RF amplifier 3forming a part of the internal stabilization system, with the NMR probe2.

RF current required for the NMR conditions is generated in block whoseoutput is connected with the RF circuits of the NMR probes 2 and 7. TheNMR signals are AF-modulated by the current produced in the modulatorsl6 and 17 whose outputs are connected respectively to the NMR probes 7and 2.

The operation of the NMR instrument of the present invention is asfollows.

After the instrument has been switched on, a test tube accommodating asample to be investigated is placed into the NMR probe 2. When workingwith the external stabilization system, the magnetic field correctioncoils 6 are connected by the switch 24 to the output of the oscillograph13. (in the drawing this position of the switch 24 is shown at A). Thechoice of the spectrum portion to be recorded, the resolution adjustmentand the setting of the optimum level of the RF and modulation frequencyvoltages, etc are carried out with the visual observation of the screenof the oscillograph 13.

The field sweep scale having been adjusted by observation of theoscillograph magnetic field correction, the coils 6 are switched over tothe recorder 14 (position B) and the spectrum is graphically recorded onthe chart paper. The current magnitude in the coils 6 and, hence, thefield intensity within the volume of the sample vary in synchronism withthe travel of the chart paper along the X-axis.

The NMR signal of the probe 7 is amplified and converted by the elements8, 20, 9, 21 and 10 of the external stabilization system and then is fedto the actuating coils ll of the external stabilization system, thuscompensating for the fluctuations which may be caused by the instabilityof the winding current of the electromagnet 1, by electrical transportfacilities, or by random movement of steel objects in the vicinity ofthe instrument, etc.

Should the necessity arise in determining the position of the lines inthe spectrum relative to the line of the reference specimen or to anyother line in the spectrum with an accuracy of :t 0.1 cps or higher, theinternal stabilization system is to be used. I

To obtain instrument operation with the ihternal stabilization system itwill suffice to adjust the line of the spectrum whose signal is selectedto be used as, the input co-ordinate in the internal stabilizationsystem so that it be in the centre of the screen of the oscillograph l3,and then to switch over the coils 6 to the output of the amplifier 5(position C).

The signal of said line after being amplified and converted by theelements 3 and 18 of the internal stabilization system and by elements12, 22, 23, 13 or 12, 22, 23 and 14, is fed to the magnetic fieldcorrection coils 5, thus compensating for the fluctuations of the NMRconditions with an accuracy higher than that ensured by the externalstabilization system.

Greater accuracy is attained dur to the fact that the source of signalsbeing recorded is confined in space to one sample to be investigated, aswell as due to the fact that the source of the stabilizing signal(reference signal) is constituted by a narrow line of high-resolutionNMR.

The NMR spectrum is recorded by sweeping the modulation frequency, whilethe signal of the line employed for stabilization is modulated by astable frequency current.

During the operation of only the external stabilization system, thefield sweep is effected with the aid of the current, for instance, inthe magnetic field correction coils 6, between which is located the NMRprobe with the sample under test. Outside the zone defined by themagnetic field correction coils 6 several millimeters away from theiredge is disposed the reference NMR probe 7 connected with the externalstabilization system.

When switching over to operating with internal stabilization, themagnetic field correction coils 6 are reconnected to the output of theinternal stabilization system and serve as an actuating unit correctingthe intensity of the field, while the recording of spectra is effectedwith the aid of frequency sweeping.

The influence of one system on the other is practically insignificant.The slight influence which yet takes place is compensated by the factthat the power lines of the magnetic flux in the coils 6 near the NMRprobes 2 and 7 are oppositely directed. Consequently, the current in themagnetic field correction coils 6 causes such a reaction of the externalstabilization system which coincides with the stabilizing effect of theinternal stabilization system in the zone of the sample under test andis opposite to said effect in the zone of the auxiliary sample.

If some external fluctuations occur for some reason in the zone of thesample under test (when working with external NMR stabilization) acurrent will appear in the magnetic field correction coils 6, which willcompensate for these fluctations. The resulting change of the NMR in thezone of the external auxiliary sample will be compensated by the currentin the actuating coils ll of the external stabilization system. At thesame time the current in the magnetic field correction coils 6 willsomewhat drop, since the fluctuations in the internal stabilizationsystem will be partly subdued by the field of the actuating coils of theexternal stabilization system. The balance is established when thecurrent in the magnetic field correction coils 6 produces for theauxiliary probe 7 a field whose value is equal to that of the correctingeffect of the external stabilization system.

Considerable advantages featured by the NMR instrument of the presentinvention become quite apparent when analyzing spectral patterns withconsiderable shifts between separate lines thereof, or spectrum groups,such as the NMR of fluorine. In this case precise determination of theposition of the lines in each spectrum group can be effected only byanalyzing each stabilizing line in succession, since usually thefrequency sweep range does not exceed 1 to 2 thousand cps.

The design of the instrument of the present invention ensures a rapidconversion from one type of stabilization to the other, with theexternal stabilization operating continuously.

As a result, the efficiency when using the proposed instrument for suchkind of work proves to be much higher than that offered by the NMRinstruments known heretofore.

The present NMR instrument is ideal for investigating temperaturedependence factors, when the stability ensured by the externalstabilization diminishes to a certain extent, when the amount ofauxiliary operations to be performed with the external stabilization(such as replacement of samples at a given temperature, preliminaryprocedures, etc) increases while the accuracy of determining the changesin the position of the lines should be extremelyhigh.

An essential advantage of the present instrument resides in that thechoice of the reference line, adjustment of the resolution, preliminarydetermination of the shift of thisline relative to the spectrum portionto be investigated, and the like operations are performed with theexternal stabilization, the internal stabilization system being madeoperative by mere switching over of the magnetic field correction coils6 to the output of the dc. amplifier 5.

The replacement of the samples with the use of the same line as thereference requires no additional operations, since with the sampleremoved, the NMR conditions remain practically unchanged due to thecontinuous operation of the external stabilization system.

We claim:

1. A nuclear magnetic resonance spectrometer with jointly functioningexternal and internal NMR stabilization systems comprising anelectromagnet, said electromagnet having poles with pole faces,magnetically remagnetic field of said electromagnet, said referenceprobe being located outside said zone defined by said coils, an externalnuclear magnetic resonance stabilization system, said external systembeing connected to said reference probe, a radio-frequency source, saidradio-frequency source being connected to said analytical and saidreference probes and producing a signal at a resonant frequency forirradiating samples of said probes, a pair of modulators, each of saidmodulators being connected to a respective one of said probes, means torecord the signal produced by said analytical nuclear magnetic resonanceprobe, and further correction coils arranged on the poles of saidelectromagnet and connected to the output of the external stabilizationsysteim 2. A nuclear magnetic resonance spectrometer as claimed in claim1, wherein said external system includes an RF amplifier having an inputand an output, an amplitude discriminator, an AF amplifier, asynchronous detector, and a dc. amplifier, said reference probe beingconnected to said input of said RF amplifier, said output of said RFamplifier being connected to said further correction coils through aseries connection of said amplitude discriminator, said AF amplifier,said synchronous detector and said do. amplifier.

3. A nuclear magnetic resonance spectrometer as claimed in claim 2,wherein said internal system com prises an RF amplifier, an amplitudediscriminator, an AF amplifier, a synchronous detector and a dc.amplifier, said analytical probe being connected to said magneticallyresponsive coil through a series connection of said RF amplifier, saidAF amplifier, said synchronous detector and said do. amplifier.

1. A nuclear magnetic resonance spectrometer with jointly functioningexternal and internal NMR stabilization systems comprising anelectromagnet, said electromagnet having poles with pole faces,magnetically responsive correction coils disposed between said poles andhaving an axis perpendicularly orientated with respect to said polefaces, an internal nuclear magnetic resonance stabilization systemhaving an output and an input, said correction coils being connected tosaid output of said internal stabilization system, an analytical nuclearmagnetic resonance probe, said analytical probe being disposed within azone defined by said coils and connected to said input of said internalstabilization system, a reference nuclear magnetic resonance probe, saidreference probe being disposed within the magnetic field of saidelectromagnet, said reference probe being located outside said zonedefined by said coils, an external nuclear magnetic resonancestabilization system, said external system being connected to saidreference probe, a radio-frequency source, said radio-frequency sourcebeing connected to said analytical and said reference probes andproducing a signal at a resonant frequency for irradiating samples ofsaid probes, a pair of modulators, each of said modulators beingconnected to a respective one of said probes, means to record the signalproduced by said analytical nuclear magnetic resonance probe, andfurther correction coils arranged on the poles of said electromagnet andconnected to the output of the external stabilization system.
 2. Anuclear magnetic resonance spectrometer as claimed in claim 1, whereinsaid external system includes an RF amplifier having an input and anoutput, an amplitude discriminator, an AF amplifier, a synchronousdetector, and a d.c. amplifier, said reference probe being connected tosaid input of said RF amplifier, said output of said RF amplifier beingconnected to said further correction coils through a series connectionof said amplitude discriminator, said AF amplifier, said synchronousdetector and said d.c. amplifier.
 3. A nuclear magnetic resonancespectrometer as claimed in claim 2, wherein said internal systemcomprises an RF amplifier, an amplitude discriminator, an AF amplifier,a synchronous detector and a d.c. amplifier, said analytical probe beingconnected to said magnetically responsive coil through a seriesconnection of said RF amplifier, said AF amplifier, said synchronousdetector and said d.c. amplifier.